No, Linux. I think I have found out how to use gphoto2 and a direct usb link instead of the capture card, which may fix it, but that'll have to run on my main computer, not my slow laptop.

I'd love to be able to tell the v4l driver for the usb capture card to just not offer the 640*480 resolution. That would fix it in a better way. Anyone have any ideas how to do that?

Are you sure you need a USB capture card? I'm using an EOS M50 and I followed along with this guide: https://www.crackedthecode.co/how-to-use-your-dslr-as-a-webc.... Works pretty well, all FOSS stuff and avoids needing a capture card.

That's ... exactly what I just said. However, the transcoding burden would be a little too much for the Atom in my laptop, so I'd have to do it on my main computer instead.

Regarding the capture card. The aspect ratio mess-up is entirely its fault.